The present invention is related in general to the field of fiber optics, and in particular, to training an optical cross-connect.
As voice calls or data are routed through a telecommunications network, information travels through many fiber-optic segments, which are linked together using cross-connects. Typically, information (e.g., packets of data) is converted from light into an electronic signal, routed to the next circuit pathway, and then converted back into light as it travels to the next network destination.
An optical cross-connect (OXC) in the physical layer of an optical network is a fundamental building block used to terminate and administer communication circuits. An OXC allows the installation of new terminal equipment by interconnecting input and output ports in an optical network. In the case of a free space optical cross connect, an array of micro electro-mechanical (MEMS) tilting mirror devices acts as the switching fabric. By adjusting the tilt angles of the MEMS mirror devices, optical signals can be directed to various destinations, i.e., to various output fibers.
The calibration, or xe2x80x9ctraining,xe2x80x9d of the several mirror-pairs, or switches, in a MEMS-mirror OXC system is a critical process in its manufacture. Because the number of switch connections for these systems scales quadratically to the number of inputs/outputs (I/O) this places great demands on the equipment used to perform training.
Prior art training equipment technology has relied heavily upon the use of numerous and costly Original Equipment Manufacturers"" (OEM) optical switch boxes and also on as many optical sources and detectors as there are I/Os. This state of the art can be improved.
This disclosure includes an opto-electronic or a fully optical circuit in which time-division-multiplexed optical signal is routed to several input ports of a MEMS-mirror Optical Cross connect (OXC). Advantageously, a single optical signal can be routed through fiber delay coils of varying lengths to introduce precise delay to an optical pulse such that the optical pulse is fed to input ports of the OXC at various timeslots. After switching the optical pulses through the OXC, the switched optical pulse at different timeslots is combined (multiplexed). The amount of optical energy in the (combined) received (output) enables the calibration or training of the OXC. The disclosed circuit may be reconfigured to measure the amount of cross talk that the OXC introduces in the system.
A single laser source is used to create a short optical pulse that is then replicated, or split, into as many pulses as there are input ports into an OXC system, for example, N pulses for N input ports. A sufficient number of delay coils producing the appropriate time delays is then used and arranged so as to ensure that each OXC input port receives a unique time-slotted pulse. Additional delay coils can be used on the output side of the OXC to ensure that irrespective of which switch path the pulses take through the OXC, the pulses will maintain a unique time-slot for that path. The N output fibers can then be directed to a single detector for detection of the pulses over a period of time specified by the total number of time-slots. Thus, for each pulse developed at the input to the training system there will be N uniquely time-slotted pulses at the output. The particular time slots that these N pulses reside in at the output will depend on the N switch connections that were made. For this one-time-slot-per-switch-connection scheme up to N2 time-slots are necessary therefore to cover all of the N2 possible switch connections that can be made.